doc(custom): fix doc description

Author: Ovilia

en/api/echarts.md

@@ -237,15 +237,50 @@ Registers a theme, should be specified when [initialize the chart instance](~ech
 
 {{ use: partial-version(version: '6.0.0') }}
 
-Register a custom series. After registration, it can be used as [series-custom.type](option.html#series-custom.type) in [setOption](~api.html#echartsInstance.setOption).
-
 ```ts
-(type: string, renderItem: Function) => void
+(type: string, renderItem: Function)
 ```
 
-+ `type` is the type of the chart to be registered, that is, the `series.type` written later in `setOption`.
+Register a custom series. After registration, it can be used in [setOption](~api.html#echartsInstance.setOption).
+
++ `type` is the type of the chart to be registered, that is, the `series.renderItem` written later in `setOption`.
 + `renderItem` is the graphic rendering logic of the custom series. For details, see [series-custom.renderItem](option.html#series-custom.renderItem).
 
+Example:
+
+```ts
+const renderItem = (params, api) => {
+    return {
+        type: 'circle',
+        shape: {
+            cx: api.coord([api.value(0), api.value(1)])[0],
+            cy: api.coord([api.value(0), api.value(1)])[1],
+            r: api.value(2) * (params.itemPayload.scale || 1)
+        },
+        style: {
+            fill: api.visual('color'),
+            opacity: params.itemPayload.opacity() || 1,
+        }
+    }
+};
+echarts.registerCustomSeries('bubble', renderItem);
+
+const option = {
+    xAxis: {},
+    yAxis: {},
+    series: {
+        type: 'custom',
+        renderItem: 'bubble',
+        itemPayload: {
+            scale: 2,
+            opacity: () => Math.random() * 0.5 + 0.5
+        },
+        data: [[11, 22, 20], [33, 44, 40], [18, 24, 10]]
+    }
+};
+chart.setOption(option);
+```
+
 ## registerLocale(Function)
 
 > Since `5.0.0`

en/option/series/custom.md

@@ -113,7 +113,7 @@ chart.on('click', {element: 'aaa'}, function (params) {
     none = true
 ) }}
 
-## renderItem(Function)
+## renderItem(Function|string)
 
 {{ use: partial-custom-renderItem-common() }}
 
@@ -493,7 +493,7 @@ Value of data item.
 
 {{ target: partial-custom-renderItem-common }}
 
-`custom series` requires developers to write a render logic by themselves. This render logic is called [renderItem](~series-custom.renderItem).
+`custom series` requires developers to write a rendering logic by themselves in the form of `Function`, or use a registered rendering logic in the form of `string` (since `v6.0.0`; See [echarts.registerCustomSeries](api.html#echarts.registerCustomSeries) for more information). This render logic is called [renderItem](~series-custom.renderItem).
 
 For example:
 

zh/api/echarts.md

@@ -234,18 +234,50 @@ echarts.registerMap('USA', usaJson, {
 {{ use: partial-version(version: '6.0.0') }}
 
 ```ts
-(type: string, renderItem: Function) => void
+(type: string, renderItem: Function)
 ```
 
-注册自定义系列。注册后可以通过 [setOption](~api.html#echartsInstance.setOption) 中使用：
+注册自定义系列。注册后可以通过 [setOption](~api.html#echartsInstance.setOption) 中使用。
+
++ `type` 注册的图表类型，也就是之后在 `setOption` 中写的 `series.renderItem`。
++ `renderItem` 自定义系列的图形渲染逻辑，详见 [series-custom.renderItem](option.html#series-custom.renderItem)。
+
+示例：
 
 ```ts
-(type: string, renderItem: Function) => void
+const renderItem = (params, api) => {
+    return {
+        type: 'circle',
+        shape: {
+            cx: api.coord([api.value(0), api.value(1)])[0],
+            cy: api.coord([api.value(0), api.value(1)])[1],
+            r: api.value(2) * (params.itemPayload.scale || 1)
+        },
+        style: {
+            fill: api.visual('color'),
+            opacity: params.itemPayload.opacity() || 1,
+        }
+    }
+};
+echarts.registerCustomSeries('bubble', renderItem);
+
+const option = {
+    xAxis: {},
+    yAxis: {},
+    series: {
+        type: 'custom',
+        renderItem: 'bubble',
+        itemPayload: {
+            scale: 2,
+            opacity: () => Math.random() * 0.5 + 0.5
+        },
+        data: [[11, 22, 20], [33, 44, 40], [18, 24, 10]]
+    }
+};
+chart.setOption(option);
 ```
 
-+ `type` 注册的图表类型，也就是之后在 `setOption` 中写的 `series.type`。
-+ `renderItem` 自定义系列的图形渲染逻辑，详见 [series-custom.renderItem](option.html#series-custom.renderItem)。
-
+[apache/echarts-custom-series](https://github.com/apache/echarts-custom-series) 项目提供了多种可以直接使用的自定义系列。
 
 ## registerLocale(Function)
 

zh/option/partial/zr-graphic.md

@@ -989,7 +989,7 @@ font: 'bolder 2em "Microsoft YaHei", sans-serif'
 
 {{ use: partial-version(version: '6.0.0') }}
 
-The union of multiple elements.
+多个图形元素并集组成的复合元素。
 
 {{ use: partial-graphic-cpt-common-props(
     type = 'compoundPath',

zh/option/series/custom.md

@@ -102,7 +102,7 @@ chart.on('click', {element: 'aaa'}, function (params) {
     none = true
 ) }}
 
-## renderItem(Function)
+## renderItem(Function|string)
 
 {{ use: partial-custom-renderItem-common() }}
 
@@ -480,7 +480,7 @@ renderItem 函数的第二个参数。
 
 {{ target: partial-custom-renderItem-common }}
 
-custom 系列需要开发者自己提供图形渲染的逻辑。这个渲染逻辑一般命名为 [renderItem](~series-custom.renderItem)。例如：
+custom 系列需要开发者以 `Function` 形式提供图形渲染的逻辑或者以 `string` 形式使用预先注册的图形渲染逻辑（从 `v6.0.0` 开始支持，详见 [echarts.registerCustomSeries](api.html#echarts.registerCustomSeries)）。这个渲染逻辑一般命名为 [renderItem](~series-custom.renderItem)。例如：
 
 ```ts
 var option = {